Emulsifiers for the preparation of aqueous polysiloxane emulsions and aqueous polysiloxane-paraffin oil emulsions with long shelf lives

ABSTRACT

Stable aqueous emulsions of polysiloxane oil and polysiloxane-paraffin oil are disclosed. The emulsifiers are alkylpolyglycosides of the formula R-O-Zn wherein R represents a linear or branched, saturated or unsaturated alkyl radical having 8-16 carbon atoms, Zn represents an alkylolilgoglycoside radical and n is 1-5. The resulting aqueous polysiloxane emulsions and polysiloxane-paraffin oil emulsions have long shelf lives.

This is a continuation of application Ser. No. 07/559,325, filed on Jul.30, 1990 now U.S. Pat. No. 5,133,897.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to emulsifiers for the preparation of polysiloxaneoil emulsions and polysiloxane-paraffin oil emulsions.

2. Discussion of the Background

Siloxane oils are used in a great many applications, for example asrelease agents, slip agents, foam inhibitors, water repellents, carriersfor skin restoratives, in plastics processing, in the glass and ceramicsindustries, in textile production and also in detergent, cosmetic anddermatological formulations. In these applications, the preferred formof the siloxane oils are as water-thinnable oil-in-water emulsions. Thepreparation of these emulsions is known to be difficult (cf. UllmannsEnzyklopadie der technischen Chemie, 3rd Ed., Vol. 15, p. 783) andusually requires water-soluble or oil-soluble agents such as alcohols oramines as disclosed in DE-A-1,033,894, and high concentrations ofemulsifiers and/or high shear forces, optionally combined with agel-like final state. A gel provides a certain stability to the emulsiondue to high viscosity, as taught in DE-A-3,024,870. Other processes forthe preparation of siloxane oil-in-water emulsions are limited torelatively low molecular weight siloxanes (DE-A-3,045,083) or can onlybe carried out at elevated temperature under vigorous evolution of gas(DE-A-2,730,923 . Obviously in the latter case, chemical changes to thepolysiloxane accompany the emulsification.

SUMMARY OF THE INVENTION

The present invention provides emulsifiers which allow the preparationof stable polysiloxane emulsions in water using low concentrations ofemulsifier, without solution aids, at low shear rates, and without theuse of elevated temperatures. This object is achieved by the use ofalkylpolyglycosides as emulsifiers for polysiloxane emulsions.

The emulsifiers are characterized in that they containalkylpolyglycosides of the formula I

    R--O--Z.sub.n                                              (I)

wherein R represents a linear or branched, saturated or unsaturatedalkyl radical having 8-16 carbon atoms, Z represents an oligoglycosideradical and n, on average, is 1-5.

Surprisingly, it has been found that these emulsifiers can be used withpolysiloxanes of different viscosities, molecular weights and chemicalstructures. Moreover, these emulsifiers have excellent biodegradabilityand very low toxicity. Surprisingly, the present emulsifiers can also beused with mixtures of polysiloxane oil and paraffin oil althoughcompounds of the formula I generally do not have a satisfactoryemulsifying action with paraffin oil. A more complete appreciation ofthe invention and many of the attendant advantages thereof will beobtained by reference to the following detailed description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention provides emulsifiers for the preparation of stable aqueouspolysiloxane oil emulsions or aqueous polysiloxane-paraffin oilemulsions. The alkylpolyglycosides used according to the inventionconform to the general formula (I)

    R--O--Z.sub.n                                              (I)

wherein R represents a linear or branched, saturated or unsaturatedalkyl radical having 8 to 16 carbon atoms, preferably 9 to 14 carbonatoms, and Z_(n) represents an oligoglycoside radical with, on average,n=1 to 5, preferably 1 to 3 hexose units or pentose units or mixturesthereof.

The invention also provides for a highly stable oil-water emulsioncomprising:

water;

one or more polysiloxane oils or a mixture of one or more polysiloxaneoils and paraffin oils; and

an alkyl polyglycoside of the formula (I)

    R--O--Z.sub.n                                              (I)

wherein R represents a linear or branched, saturated or unsaturatedalkyl radical having 8-16 carbon atoms, Z_(n) represents anoligoglycoside radical, and n is 1-5, wherein the quantity of oil isabout 1-68% by weight based on the total weight of water and oil; andthe emulsion is stable upon standing for at least two months.

The invention also provides for a method for preparing the highly stableoil-water emulsion, the method comprising: dispersing an effectiveamount of an alkyl polyglycoside of the formula (I) in polysiloxane oilor a mixture of polysiloxane and paraffin oil; and

admixing water; wherein the quantity of oil is about 1-68% by weightbased on the total weight of water and oil.

Particular preference is given to linear standard alkylpolyglycosideshaving 10 to 14 carbon atoms and with a degree of glycosidation ofbetween 1.1 and 2.0.

The alkylpolyglycosides used according to the invention can be preparedwholly or partly based on renewable raw materials by known processes.For example, dextrose is reacted in the presence of an acidic catalystwith n-butanol to form butyloligoglycoside mixtures which are thenconverted to the desired alkyloligoglycosides with long-chain alcoholsin the presence of an acidic catalyst. The formula of the products canvary within certain limits. The alkyl radical R is determined by thechoice of long-chain alcohol. It is advantageous on economic grounds touse the industrially accessible surfactant alcohols having 8 to 16carbon atoms, for example natural alcohols from the hydrogenation offatty acids or fatty acid derivatives, Ziegler alcohols and oxoalcohols.

The oligoglycosyl radical Z_(n) is determined by the selection of thecarbohydrate and by the regulation of the average degree ofoligomerisation, n, for example according to DE-A-1,943,689. Inprinciple, it is possible to convert known polysaccharides,oligosaccharides and monosaccharides such as starch, maltodextrin,dextrose, galactose, mannose and xylose into alkylpolyglycosides.Particular preference is given to the industrially accessiblecarbohydrates starch, maltodextrin and dextrose. Since the industriallyrelevant alkylpolyglycoside syntheses are not regioselective orstereoselective, the alkylpolyglycosides are always mixtures ofoligomers which in turn are mixtures of different isomeric structures.Pyranose and furanose structures are present side by side and have bothα- and β-glycosidic linkages. Even the linkage positions differ betweenpairs of saccharide radicals Depending on the method of synthesis, thealkylpolyglycosides may also contain associated substances such asresidual alcohols, monosaccharides, oligosaccharides andoligoalkylpolyglycosides.

Ecologically the alkylpolyglycosides are among the most gentlesurfactants, which is of particular interest for cosmetic andpharmaceutical applications of polysiloxane oils andpolysiloxane-paraffin oil mixtures. For instance, tests ofbiodegradability in the coupled unit test gave DOC-degradation values of95 to 97%.

Toxicity data shows an LD 50 (rat)>10,000 mg/kg, LC 50 (Golden orfe) of12-40 mg/l and EC 50 (daphnia) of 30-110 mg/l for both C₁₀ -C₁₂ - andC₁₂ -C₁₄ -alkylpolyglycosides. This data, indicates excellent ecologicalsafety compared with many other surfactants.

Throughout this disclosure "gentle" shear forces refers to the typicalsheer forces generated in the normal chemical laboratory using amagnetic stir bar or manual agitation. The preferred method forpreparing the emulsion comprises dissolving or dispersing the emulsifierat room temperature in the polysiloxane oil or polysiloxane-paraffin oilmixture by applying gentle shear forces. Usually these fluids have aslight opacity which remains constant for days. Then, again using onlygentle shear forces, water is admixed with the solution or dispersionwith stirring. The emulsions obtained by this method are generally whiteto bluish-white and stable for months. In a few cases creaming isobserved and can be eliminated by gentle shearing.

The emulsifier concentration relative to the oil phase is usuallybetween 2 and 40%, preferably between 5 and 30%, the determining factorbeing economy. The water/oil ratio is usually between 100 and 0.2,preferably between 50 and 0.3, and the viscosity of the emulsionincreases with an increasing proportion of the dispersed phase.

If desired it is possible to add other surfactants as coemulsifiers tothe alkylpolyglycoside. Suitable surfactants include: anionic types suchas long chain fatty carboxylic acids and sulfates; the cationic typessuch as alkyl ammonium salts; the zwitterionic types such as alkylammonium carboxylates and alkyl amine oxides; and the nonionicsurfactants such as alkyl esters and ethers. However, the additionalsurfactants, if any, are not used in an amount greater than 50% byweight, relative to the alkylpolyglycosidic surfactants.

Having generally described this invention a further understanding can beobtained by reference to some specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

EXAMPLES Example 1

5 g of a C₁₀ -C₁₂ -alkylpolyglycoside (proportion of active substance46%, C₁₀ /C₁₂ 4:1, average D.P. 1.3 determined by ¹ H-NMR) weredispersed at room temperature in 10 g of polydimethylsiloxane oil ofviscosity 500 c St, with gentle stirring, in the course of about 20 sec.Then 85 ml of deionized water was admixed over 1 to 2 minutes bystirring with the slightly viscous dispersion. A bluish-white emulsionformed, which showed no sign of instability even after standing for 2 to3 months.

EXAMPLE 2

5 g of a C₁₂ -C₁₃ -alkylpolyglycoside (proportion of active substance55%, C₁₂ /C₁₃ 41:58, average D.P. 1.2) were dispersed at roomtemperature in 10 g of a 1:1 mixture of polydimethylsiloxane oil ofviscosity 500 o St and a DAB 6 Paraffin oil of viscosity 140 c St, i.e.,conforming to Federal German Pharmacopoeia, 6th Ed. Then 85 ml ofdeionized water was admixed with stirring as in Example 1. A whiteemulsion formed which was stable for months. This result is surprisingsince a similar experiment with pure paraffin oil resulted in separationof the emulsion, with creaming, after only minutes and completeseparation after about 1 hour.

EXAMPLES 3 to 13

Examples 3 to 13 were carried out in an identical manner as Example 1.They illustrate the effective emulsification of polysiloxane oil to formoil-water emulsions using the alkylpolyglycosides of the presentinvention with variation of the polysiloxane oil, the emulsifierstructure, the concentration, and the water-oil ratio. The results areshown in Table 1 where all quantities are reported in grams.

EXAMPLE 14

1.2 g of alkylpolyglycoside C₁₀, C₁₃, G₁.6 and 1.15 g of MARLIPAL® 24/50(a C₁₂ -C₁₄ -fatty alcoholethoxylate with 5 mol of ethylene oxide/mol)were dispersed in 10 g of a 1:1 mixture of dimethylpolysiloxane oil ofviscosity 500 c St and a DAB 6 Paraffin oil of viscosity 140 c St, i.e.,conforming to Federal German Pharmacopoeia, 6th Ed. Then, as in Example1, water was admixed with stirring. A white emulsion formed which had ahigh stability. In contrast, the ethoxylate alone has no emulsifyingeffect on the present oil-in-water system.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

                                      TABLE 1                                     __________________________________________________________________________                 Example                                                          Composition  3  4  5  6  7  8  9  10 11 12 13                                 __________________________________________________________________________    Dimethylpolysiloxane oils                                                     Visc. 100 c St                                                                             10                                                               250             10                                                            500                         5  5  5  35 3.3                                                                              60                                 2000               10                                                         Dimethylpolysiloxane oil                                                                            10 5                                                    Visc. 200 c St                                                                Parafin oil DAB 6,       5  5  5  5     6.7                                   Visc. 140 c St                                                                Water        88 88 88 88 88 88 87 89 60 88 28                                 C.sub.10 C.sub.12 APG (G.sub.1.3)                                                          2.3                                                                              2.3                                                                              2.3                                                                              2.3         1  4.6                                                                              2.3                                                                              12                                 C.sub.12 C.sub.13 APG (G.sub.1.2)                                                                      2.3                                                  C.sub.12 C.sub.13 APG (G.sub.1.2)                                                                            2.5                                            C.sub.12 C.sub.14 APG (G.sub.1.2)                                                                         2.4                                               Emulsion stability*                                                                        ++ ++ ++ ++ ++ +  ++ ++ ++ ++ ++                                 after 3 days                                                                  __________________________________________________________________________     * ++ Very stable, + stable, slight but readily redispersible creaming    

What is claimed an new and desired to be secured by Letters Patent ofthe Unites States is:
 1. A highly stable oil-water emulsioncomprising:water; one or more polysiloxane oils or a mixture of one ormore polysiloxane oils and paraffin oils; and an alkylpolyglycoside ofthe formula (I)

    R--O--Z.sub.n                                              (I)

wherein R represents a linear or branched, saturated or unsaturatedalkyl radical having 8-16 carbon atoms, Z_(n) represents anoligoglycoside radical, and n is 1-5; wherein the quantity of oil isabout 1-68% by weight based on the total weight of water and oil; andthe emulsion is stable upon standing for at least two months.
 2. Theemulsion of claim 1, wherein R is a linear, saturated alkyl radicalhaving 10-14 carbon atoms, Z_(n) is an oligoglycoside radical, and n is1.1 to 2.0.
 3. The emulsion of claim 1, further comprising acoemulsifier selected from the group consisting of anionic, cationic,zwitterionic and non-ionic surfactants.
 4. A method for preparing thehighly stable oil-water emulsion of claim 1 comprising:dispersing aneffective amount of an alkylpolyglycoside of the formula (I) inpolysiloxane oil or a mixture of polysiloxane and paraffin oil; andadmixing water; wherein the quantity of oil is about 1-68% by weightbased on the total weight of water and oil.